Embodiments of the invention relate generally to a system for improved backlight illumination uniformity in display devices.
Large format display devices, such as flat panel liquid crystal displays (LCDs) typically utilize cold cathode fluorescent lamps (CCFL) as light sources. Although CCFLs have small form factors (with diameters typically in the 2.6 to 3.0 mm range) CCFLs have relatively low luminous efficiency and are fragile at longer lengths. As display panel screen diagonals continue to increase there is also an increasing need for mechanically robust, high luminous efficiency light sources to illuminate such displays.
More recently, hot cathode fluorescent lamps (HCFL) have been used as light sources for such flat panel displays. The use of HCFL's allows for current pulsing of the light output which allows for the reduction of motion blur caused by the finite lag time for the LCD pixel to change state between image frames. HCFLs further provide higher luminous efficiency than CCFLs and are more mechanically robust for longer tube lengths (having typical diameters of around 16 mm). However, since the trend in flat panel displays is to reduce panel depth and HCFLs have larger diameters than CCFLs, the HCFLs tend to occupy more space within the backlight cavities of the display panels. This causes greater non-uniformity in the illumination under the LCD screen in the form of banding, which is generally objectionable to end users. Furthermore, since the trend in flat panel displays is to reduce panel depth there is a general desire to increase uniformity of illumination without significantly increasing the depth of the backlight cavity.